Natural gas hydrates (NGHs) are ice-like compounds formed by natural gas and water under specific thermodynamic conditions, and are a special form of natural gas in the nature. The investigation revealed that a large amount of NGHs are distributed in the terrestrial permafrost and the deep-sea marine sediments, wherein the total resource quantity of methane is up to 2.1*1016 m3. Natural gas is a kind of clean energy resource and is favorable for environmental protection and sustainable development, so it has the practical significance in researching how to effectively exploitate the natural gas hydrates.
The natural gas hydrates may exist in the nature in kinds of forms. The natural gas hydrates are solid when being buried in the ocean bed, and are changed from solid to gas when its molecular structure is changed in the exploitation process, that is to say, the hydrates are subjected to phase change in the exploitation process. Based on the characteristics of the natural gas hydrates, the exploitation method of the natural gas hydrates is different from that of the conventional energy resources. At present, most methods related to the exploitation of natural gas hydrates is to decompose the natural gas hydrates buried in the sediments at first and then transport the decomposed natural gas to the ground. At present, the general exploitation method of the natural gas hydrates is to break the temperature and pressure conditions for the its stable existence and make it to decompose. The methods mainly include the depressurization, the thermal stimulation and the chemicals injection. The decomposition of the natural gas hydrates by these methods will increase the pore pressure and liquefy the sediments in the hydrate reservoir. Meanwhile, there is no filler in the pores in sediments after the hydrates are produced. These may cause the uniform or localized compaction or localized shear of the hydrate stratum, resulting in the gradually damage and lower stabilization of the hydrate reservoir. The lowered reservoir stabilization will increase the risk for submarine landslide and large-scale collapses. Recently, the CO2 replacement method has attracted great attention. Experimental researches have demonstrated the replacement of CH4 in the hydrate cavities with CO2, succeeded in both CH4 recovery and CO2 sequestration. The exchange of CH4 in hydrate by CO2 will also increase the stability of the reservoir sediments as well as maintain hydrates in the solid state.
Since the geological conditions, the components and the formation mechanisms of the natural gas hydrates at different regions have great discrepancy, the exploration and exploitation of the hydrate are generally guided by the experimental simulations. However, the present experimental equipments are relatively simple and difficult to satisfy the requirements of the researches on the stratum stability in the exploitation process of the natural gas hydrates. Meanwhile, there is few professional simulation laboratories which are completely used to research the stratum stability in the exploitation of the natural gas hydrates buried in the sediments. Particularly, a three-dimensional simulation research device for stratum stability in the exploitation process of the natural gas hydrates has not been reported.